In the production sector of kitchen towels rolls of tissue paper are now established two different double embossing contrasted processes with lamination of the plies that have had moments of greater or worse success over the years: these are the NESTED method, in which the tips of one of the two plies lurk between the tips of the other ply, and the TIP/TIP method, in which the tips of a ply are glued against the other ply tips, both well known to the sector's operators.
To date, the NESTED method is undoubtedly the most widespread and almost universally used for the production of kitchen paper rolls. This method allows a very simple machining without problems of rollers duration, of rollers temperatures, of weaknesses in the contact between the latter.
A conventional type of machinery for the production of two-ply embossed towel paper rolls with NESTED technology is schematically shown in FIG. 1. In this, a first, V1, and a second ply of tissue paper, V2, are dragged by a group of rollers which perform the embossing, the pairing and the bonding of the two plies. More specifically, each ply crosses a relative deflection roller, R1, R2, a relative contrast roller, C1, C2, and a relative engraving roller, G1, G2, the interaction between which perform the NESTED pairing of the two plies V1 and V2. In correspondence of a first engraving roller G1 it is present a group of application of the glue comprising a glue tank, S, in which catches a buffer roller, T, which transfers the glue to an applicator roller, A, which applies the glue on the surface of the first ply V1. Before leaving the first engraving roller G1 the two paired paper plies are pressed one against the other by a pressing roller, P, which acts against the first engraving roller G1 to allow the glue to bind together the two plies before leaving the machinery through a further deflection roller, R3.
This type of conventional machinery, however, presents a universally known problem with which manufacturers are willing to live, given the operational advantages that this offers compared to the TIP/TIP method: the two sides of the laminated two-ply paper that is obtained have a different “feel” because one is perfectly smooth (because housed in the engraving roller) while the other is rougher because “double embossed” by the action of the pressing roller P (known in the industry as Marrying Roll) which presses the second ply V2 on the tips of the engraving roller G1 to allow the bonding. This defect is also clearly visible because while one face presents the decoration very clearly impressed by the embossing, the other presents a very confusing look and often it is not possible to perceive the embossing pattern of the roller that generated it because it is confused with the double embossing of the first roller G1. In the detail of FIG. 1, which represents an enlarged view of a paper portion output from the pressing roller, it is possible to observe how the side in contact with the pressing roller P itself has the aforesaid roughness effect due to the decomposition into at least two flat surfaces, S1, S2, on two different levels.
This problem has been repeatedly addressed over times with various attempts of solution.
A type of pressing roller P initially used was made of steel. The extremely hard surface allowed to avoid the effect of double embossing and however it was extremely difficult to obtain a uniform contact over the entire width of the ply because they arose big problems of pressure and bending of the rollers as it was necessary that the pressure of the pressing roller P against the engraving roller G1 was extremely high so that the rollers themselves were extremely robust in order to avoid the bending, with very high production costs and dragging difficulties because of the few tips in contact as well as with an enormous difficulty having a uniform contact along the entire width of the ply. To overcome this problem, a conventional type of pressing roller P involves the use of a steel roller with a rubber cover. Subsequently, in order to avoid the effect of double embossing caused by the yielding of the rubber, this rubber cover has been raised to levels of hardness rather high such as 70 SHA and again after this coverage was improved by adopting a double layer of rubber, a softer inside and a harder outside. This way, it was sought to reduce the effect of double embossing due to the superficial yielding of the rubber without, however, preventing the overall yielding of the roller surface and its deformability necessary in order to properly adjust the bonding pressure and to determine the correct nip. However, this solution has proved to be inefficient due to the impossibility to find the kinds of rubbers to be paired making it possible to obtain the desired elastic response characteristics of the roller and of its surface.
In all the above said solutions the pressing roller P requires a structure such as to be able to contrast the bending of the rollers involved in the process, but this structure involves a weight and a significant inertia which contrast the dragging of the roller itself by the engraving roller; for this reason, even if the value of the pressure required to pair the two plies may be relatively low, it is actually necessary to force much more the contact between the rollers to ensure the rotation start of the pressing roller P, which is one of the double embossing causes.
To overcome this problem they have also been proposed pressing roller provided with convex or concave outer surface to compensate the bending but this imposes the necessity to operate always with the same pressures between the various rollers to obtain a uniform bonding over the entire width of the paper.
In the field of handling of paper or other material they are conventionally known dragging wheels which are made, or superficially coated, with rubber material or other plastic material having certain hardness and flexibility characteristics, in which a good deformability is obtained thanks to a particular constructive geometry. Dragging wheels of this type are described for example in British Patent GB 1205097A and in the European patent application EP 2803610 A1 and comprise a metal tubular core on which it is integrally mounted a rubber coating material of thickness high enough to allow to obtain in said thickness a series of axial cavities arranged radially inclined. The rubber material coating has a very high deformability allowed by the particular “lightened” geometry of the coating itself in which the separation septa between successive cavities are elastic elements that allow a high deformability of the surface. Wheels of this type have conventionally the very outer diameter greater than the axial width and are used to support and move the advancing of paper material or the like in a configuration in which a plurality of the above said wheels with axial width much smaller than the width of the tape to be supported are arranged coaxially spaced apart by a certain entity.